This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | -6 |
| 4 | 35 |
| 5 | -225 |
| 6 | 1624 |
| 7 | -13132 |
| 8 | 118124 |
| 9 | -1172700 |
| 10 | 12753576 |
| 11 | -150917976 |
| 12 | 1931559552 |
| 13 | -26596717056 |
| 14 | 392156797824 |
| 15 | -6165817614720 |
| 16 | 102992244837120 |
| 17 | -1821602444624640 |
| 18 | 34012249593822720 |
| 19 | -668609730341153280 |
| 20 | 13803759753640704000 |
| 21 | -298631902863216384000 |